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	<!--<script>
		//可以不赋值
		let as
		console.log(as);
		//不能重复命名
		let a="xiaozhi"
		let a="bianliang"
		//块级作用域有效
		{
			let b="12"
		}
		console.log(b);
		//不能被变量提升
		console.log(c);
		let c=12
		//不影响作用域
		function fn(){
			let d=34
			return function(){
				console.log(d);
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	<script>
	   const a=12
	   a=13
	   console.log(a);
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